1. Field of the Invention
The present invention relates to a lithographic apparatus. The invention further relates to a method of manufacturing a device, as well as a device manufactured thereby.
2. Brief Description of Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. comprising part of, one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and so-called scanners, in which each target portion is irradiated by scanning the pattern through the projection beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti parallel to this direction.
The known apparatus comprises a collector for collecting radiation from a radiation source. The collector is arranged for transmitting the collected radiation to an illumination system. The illumination system is arranged for providing a projection beam of radiation, which is used for applying a desired pattern onto a target portion of a substrate. The collector comprises for example suitable radiation reflecting mirror shells. Such a collector is known from the European patent application EP 1225481, which is incorporated herein by reference. Particularly, the collector is arranged to focus incoming radiation, received from the radiation source, onto a small focusing area or focussing point.
A disadvantage of the known apparatus is, that the collector is heated up by the incoming radiation, each time the respective radiation source is switched on. As a result, the collector expands, leading to a shift in direction of the outgoing radiation and/or a translation of the focussing point of the radiation and distortion of a resulting illumination beam. Consequently, it is difficult or impossible for the illuminating system to generate a projection beam of radiation with certain desired characteristics, having for instance a suitable homogeneity, radiation distribution, beam direction, beam intensity, beam cross-section and the like. Besides, the distortion of the projection radiation, caused by the thermal expansion of the collector, hampers the manufacturing of devices with a desired high precision.